Work, Levers and Torque
Isotonic contractions do
is the distance moved in the direction of the force, multiplied by the
force. There is no work done in an isometric contraction.
W = F*D
Muscles can only
contract about 20% of their length. To provide a larger range of
motion, levers are used to provide torque . The contracting muscle
creates a tension (T) at an angle(θ) to the bone (the moment or lever
arm), and at a certain distance(d). This creates a torque (τ)
around the joint (the fulcrum).
a force, the torque is greater when
the force is applied further from the joint.
In your arm the
force of the bicep is fairly close to the joint, and the downward
force of an object in your hand is relatively far from the joint.
This means that an object in your hand exerts a much
downward than your muscle does upward given equal
Your bicep muscle has to provide a
much larger force to overcome the torque produced by an object to do
The 5kg mass is 10 times further from the joint than the muscle force,
therefore the muscle force has to be at least 10 times greater to do
work on the object.
A tension of 550N is applied to move the mass up 10cm.
The work done on the mass is equal to F*h.
550N*0.01m = 5.5 Nm.
Image modified by Kelsey